Abstract:

An installation for conveying superheated fluid discharged from a vent
located at or near the base of a body of water. The installation
comprises a hood for locating the installation over the vent, and an
insulated conduit that is in fluid communication with the hood and
extends upwardly through the body of water.

Claims:

1. An installation for conveying superheated fluid discharged from a vent
located at or near the base of a body of water, the installation
comprising:a hood for locating the installation over the vent; andan
insulated conduit that is in fluid communication with the hood and
extends upwardly through the body of water.

2. An installation according to claim 1, wherein the conduit comprises a
series of cylindrical sections, the internal diameter of the cylindrical
sections increasing with distance from the hood.

3. An installation according to claim 2, wherein the series of cylindrical
sections is configured to maintain an approximately constant fluid
velocity within the conduit.

4. An installation according to claim 2, wherein the series of cylindrical
sections is constructed such that the pressure tolerance of sections
within the series increases with distance from the hood.

5. An installation according to claim 2, wherein the conduit further
comprises one or more conical sections that interconnect adjacent
cylindrical sections within the series.

6. An installation according to claim 5, wherein the series of cylindrical
sections and the one or more conical sections are configured to maintain
an approximately constant fluid velocity within the conduit.

7. An installation according to claim 5, wherein the series of cylindrical
sections and the one or more conical sections are constructed such that
the pressure tolerance of sections within the series increases with
distance from the vent.

8. An installation according to claim 2, wherein the upper end of the
cylindrical section that is connected to the hood is positioned at
approximately the same depth as the depth of vapourization of fluid
conveyed through the conduit.

9. An installation according to claim 1, wherein the hood is thermally
insulated.

10. An installation according to claim 1, wherein the hood includes an
overflow discharge.

11. An installation according to claim 10, wherein the overflow discharge
is in the form of one or more holes located around the base of the hood.

12. An installation according to claim 1, further comprising a series of
buoys and/or anchors attached to the insulated conduit to maintain the
conduit in a generally constant configuration.

13. An installation according to claim 1, further comprising a heat engine
that converts energy within the fluid exhausted from the conduit into
mechanical motion.

14. An installation according to claim 13, wherein the heat engine is
located at or above the surface of the body of water.

15. An installation according to claim 1, wherein the body of water is the
sea, and the vent is located on or near the sea floor.

16. An installation according to claim 15, wherein the upper end of the
insulated conduit terminates below the sea surface, such that fluid can
be exhausted from the insulated conduit into the upper layers of the sea.

17. An installation according to claim 16, wherein the fluid exhausted
from the insulated conduit creates a plume which causes the transport of
surrounding sea water from one level in the sea to a higher level.

18. An installation according to claim 15, further comprising a bubble
pump located beneath the sea surface, and the upper end of the insulated
conduit terminates inside the bubble pump, such that fluid exhausted from
the conduit drives the bubble pump.

19. An installation according to claim 18, wherein the bubble pump
comprises a thin walled conduit.

20. An installation according to claim 1, wherein the vent is a natural
hydrothermal vent.

21. An installation according to claim 1, further comprising a nuclear
reactor that heats fluid that is discharged from the vent.

22. A combined installation for conveying superheated fluid discharged
from a plurality of vents located on the sea floor, the combined
installation comprising a plurality of individual installations each
comprising a hood for locating the individual installation over a vent,
and an insulated conduit that is in fluid communication with the hood and
extends upwardly through the body of water, the hood of each individual
installation being located over a respective one of the vents, and the
upper ends of the insulated conduits of the individual installations
being arranged below the sea surface to form a vertical set of plumes.

23. A method of conveying thermal energy from a vent located at or near
the base of a body of water, the vent discharging superheated fluid, the
method comprising the steps of:a) installing an installation over the
vent, the installation comprising a hood that is in fluid communication
with an insulated conduit, such that superheated fluid discharged from
the vent is directed by the hood into the insulated conduit; andb)
conveying fluid upwardly in the insulated conduit and through the body of
water.

24. A method according to claim 23, wherein step (b) further comprises
conveying the fluid in a manner such that the fluid at least partly
vapourizes as it rises within the conduit.

25. A method according to claim 23, wherein the fluid at the upper end of
the insulated conduit is at least a two-phase fluid.

26. A method according to claim 25, wherein the installation further
comprises a heat engine that receives fluid exhausted from the conduit,
and the method further comprises converting the enthalpy of the fluid
into mechanical energy in the heat engine.

27. A method according to claim 25, wherein the body of water is the sea,
and the method further comprises discharging fluid from the conduit below
the sea surface such that the buoyancy of the at least two-phase fluid
creates a plume that mixes sea water between different levels by
entrainment within the plume.

28. A method according to claim 25, wherein the body of water is the sea
and the installation further comprises a bubble pump located beneath the
sea surface and the upper end of the insulated conduit terminates inside
the bubble pump, and the method further comprises discharging the at
least two-phase fluid from the conduit inside the bubble pump to drive a
bubble pump and create an upward flow of water through the bubble pump.

29. A method according to claim 27, whereby deep water containing
nutrients are brought into the well-lit upper layers of the sea so as to
increase the productivity of photosynthesizing organisms.

30. A method according to claim 29, whereby a marine ecosystem is created
or enhanced in order to increase fish catch.

31. A method according to claim 29, whereby a marine ecosystem is created
or enhanced in order to export carbon dioxide from the atmosphere by
increased photosynthesis.

32. A method according to claim 27, comprising mixing layers of the sea in
order to bring deep water of high alkalinity toward the sea surface and
increase the solubility of carbon dioxide in the mixed layer.

33. A method according to claim 32, further comprising dissolving carbon
dioxide from the atmosphere in the sea.

34. A method according to claim 23, wherein the installation further
comprises a nuclear reactor, and the method further comprises heating
fluid using energy generated by the reactor, the heated fluid being
discharged from the vent.

Description:

BACKGROUND OF THE INVENTION

[0001]The present invention relates to an installation for conveying
superheated fluid that is discharged from a vent located at or near the
base of a body of water.

[0002]It is known to utilize geothermal energy for heating, power
generation and desalination. In these applications, the energy is
conveyed in the form of heat from a location beneath the Earth's surface
to a facility on the Earth's surface, which utilizes that energy for its
desired purpose.

[0003]These applications use geothermal energy that is brought to the
Earth's surface through vents or cracks, or through wells specifically
drilled into the Earth's surface. For many reasons, including the
accessibility of vents, existing facilities that utilize geothermal
energy are land based and located near vents, etc. that are also formed
in land, as opposed to in the sea floor.

[0004]Geothermal energy is also released through natural hydrothermal
vents in the sea floor that discharge water heated by the geothermal
energy.

[0005]Hydrothermal vents fed by geothermal energy can be found in
mid-oceanic ridges, which are typically at depths of 2000 metres or
greater below sea level. Vents in these locations typically discharge
fluid at temperatures in the order of 350° C. to 400° C.
Hydrothermal vents that are also fed by geothermal energy can be found in
volcanic arcs, which are typically at depths of approximately 150 to 400
metres below sea level. Vents in these locations typically discharge
fluid at temperatures in the order of 160° C. to 200° C.

SUMMARY OF THE INVENTION

[0006]The present invention has been conceived to utilize energy of heated
water discharged from a vent located at or near the base of a body of
water. The vents can be natural hydrothermal vents or artificial vents
fed by artificial underwater heat sources.

[0007]The present invention provides an installation for conveying
superheated fluid discharged from a vent located at or near the base of a
body of water, the installation comprising: [0008]a hood for locating
the installation over the vent; and [0009]an insulated conduit that is in
fluid communication with the hood and extends upwardly through the body
of water.

[0010]Thus, heated fluid that is discharged from the vent is captured by
the hood and directed into the insulated conduit, which directs the fluid
upwardly towards the surface of the body of water, or land above or
adjacent the body of water.

[0011]In certain embodiments, the conduit comprises a series of
cylindrical sections, the internal diameter of the cylindrical sections
increasing with distance from the hood.

[0012]The series of cylindrical sections can be configured to maintain an
approximately constant fluid velocity within the conduit.

[0013]Alternatively or additionally, the series of cylindrical sections
can be constructed such that the pressure tolerance of sections within
the series increases with distance from the hood.

[0014]In some embodiments, the conduit further comprises one or more
conical sections that interconnect adjacent cylindrical sections within
the series.

[0015]In such embodiments, the series of cylindrical sections and the one
or more conical sections are configured to maintain an approximately
constant fluid velocity within the conduit.

[0016]Alternatively or additionally, the series of cylindrical sections
and the one or more conical sections are constructed such that the
pressure tolerance of sections within the series increases with distance
from the vent.

[0017]In certain embodiments, the upper end of the cylindrical section
that is connected to the hood is positioned at approximately the same
depth as the depth of vapourization of fluid conveyed through the
conduit.

[0018]In certain embodiments, the hood is thermally insulated.

[0019]The hood may be provided with an overflow discharge.

[0020]Thus, if the rate of flow of fluid entering the conduit is lower
than the rate of flow of superheated fluid discharged from the vent, the
excess fluid can be discharged through the overflow discharge.

[0021]In certain embodiments, the overflow discharge may be in the form of
one or more holes located around the base of the hood.

[0022]The installation may further comprise a series of buoys and/or
anchors attached to the conduit to maintain the conduit in a generally
constant configuration.

[0023]In certain embodiments, the installation may further comprise a heat
engine that converts energy within the fluid exhausted from the conduit
into mechanical motion.

[0024]The heat engine may be located at or above the surface of the body
of water. In these embodiments, the upper end of the conduit may
terminate at or above the surface of the body of water.

[0025]In some applications, the body of water is the sea, and the vent is
located on or near the sea floor.

[0026]Preferably, the upper end of the conduit may terminate below the sea
surface, such that fluid can be discharged from the conduit into the
upper layers of the sea.

[0027]Preferably, fluid exhausted from the insulated conduit creates a
plume which causes the transport of surrounding sea water from one level
in the sea to a higher level.

[0028]In some alternative embodiments, the installation further comprises
a bubble pump located beneath the sea surface, and the upper end of the
conduit terminates inside the bubble pump, such that fluid exhausted from
the conduit drives the bubble pump.

[0029]Preferably, the bubble pump comprises a thin walled conduit.

[0030]In some embodiments, the vent is a natural hydrothermal vent.

[0031]In some alternative embodiments, the installation further comprises
a nuclear reactor that heats fluid that is discharged into the conduit
through the vent and hood combination or other connector.

[0032]The present invention also provides an installation for conveying
superheated fluid discharged from a plurality of vents located on the sea
floor, the installation comprising a plurality of installations as
described above, the hood of each installation being located over a
respective one of the vents, the upper ends of the insulated conduits of
the installations being arranged below the sea surface to form a vertical
set of plumes.

[0033]The present invention also provides an installation for conveying
superheated fluid discharged from a plurality of vents located on the sea
floor, the installation comprising a plurality of installations as
described above, the hood of each installation being located over
respective vents, the upper ends of the insulated conduits of the
installations being arranged below the sea surface to form a horizontal
array of plumes.

[0034]The present invention also provides a method of conveying thermal
energy from a vent located at or near the base of a body of water, the
vent discharging superheated fluid, the method comprising the steps of:
[0035]a) installing an installation over the vent, the installation
comprising a hood that is in fluid communication with an insulated
conduit, such that superheated fluid discharged from the vent is directed
by the hood into the insulated conduit; and [0036]b) conveying fluid
upwardly in the insulated conduit and through the body of water.

[0037]Preferably, step (b) further comprises conveying the fluid in a
manner such that the fluid at least partly vapourizes as it rises within
the conduit.

[0038]Preferably, such that fluid at the upper end of the insulated
conduit is at least a two-phase fluid.

[0039]In embodiments in which the installation further comprises a heat
engine that receives fluid exhausted from the conduit, the method can
further comprise converting the enthalpy of the fluid into mechanical
energy in the heat engine.

[0040]In some embodiments in which the body of water is the sea, the
method can further comprise discharging fluid from the conduit below the
sea surface such that the buoyancy of the at least two-phase fluid
creates a plume that mixes sea water between different levels by
entrainment within the plume.

[0041]In embodiments in which the body of water is the sea and the
installation further comprises a bubble pump located beneath the sea
surface and the upper end of the insulated conduit terminates inside the
bubble pump, the method can further comprise discharging the at least
two-phase fluid from the conduit inside the bubble pump to drive a bubble
pump and create an upward flow of water through the bubble pump.

[0042]The installation and method can be configured such that deep water
containing nutrients can be brought into the well-lit upper layers of the
sea so as to increase the productivity of photosynthesizing organisms.

[0043]In such embodiments, a marine ecosystem may be created or enhanced
in order to increase fish catch.

[0044]Alternatively or additionally, a marine ecosystem is created or
enhanced in order to export carbon dioxide from the atmosphere by
increased photosynthesis.

[0045]The method may further comprise mixing layers of the sea in order to
bring deep water of high alkalinity toward the sea surface and increase
the solubility of carbon dioxide in the mixed layer.

[0046]The method may further comprise dissolving carbon dioxide from the
atmosphere in the sea.

[0047]In embodiments in which the installation further comprises a nuclear
reactor, the method can further comprise heating fluid using energy
generated by the reactor, the heated fluid being discharged into the
conduit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0048]In order that the invention may be more easily understood,
embodiments will now be described, by way of examples only, with
reference to the accompanying drawings, in which:

[0049]FIG. 1: is a schematic view showing three installations according to
a first embodiment of the present invention;

[0050]FIG. 2: is a chart showing pressure as a function of depth for an
installation according to an embodiment of the present invention with an
intake depth of 200 m;

[0051]FIG. 3: is a chart showing temperature plotted a function of depth
for an installation according to an embodiment of the present invention
with an intake depth of 200 m;

[0052]FIG. 4: is a chart showing specific volume as a function of depth
for an installation according to an embodiment of the present invention
with an intake depth of 200 m;

[0053]FIG. 5: is a chart showing steam quality as a function of depth for
an installation according to an embodiment of the present invention with
an intake depth of 200 m;

[0054]FIG. 6: is a chart showing pressure as a function of depth for an
installation according to an embodiment of the present invention with an
intake depth of 2500 m;

[0055]FIG. 7: is a chart showing temperature as a function of depth for an
installation according to an embodiment of the present invention with an
intake depth of 2500 m;

[0056]FIG. 8: is a chart showing specific volume as a function of depth
for an installation according to an embodiment of the present invention
with an intake depth of 2500 m;

[0057]FIG. 9: is a chart showing steam quality as a function of depth for
an installation according to an embodiment of the present invention with
an intake depth of 2500 m;

[0058]FIG. 10: is a schematic view of an installation according to a
second embodiment of the present invention; and

[0059]FIG. 11: is a schematic view of an installation according to a third
embodiment of the present invention.

DETAILED DESCRIPTION

[0060]FIG. 1 shows three installations 10, each in accordance with a first
embodiment of the present invention. Each of these installations is
arranged to convey superheated fluid discharged from a vent 12a, 12b, 12c
located at the base of a body of water. In this embodiment, the body of
water is the sea, and the vents 12a, 12b, 12c are natural hydrothermal
vents located on the sea floor. Each installation has a hood 14 for
locating the installation 10 over one of the vents. A conduit 16 in fluid
communication with the hood 14 extends upwardly through the sea and
towards the sea surface S.

[0061]The hood 14 anchors the lower end of the conduit 16 over the vent
12, and collects and directs fluid, in the form of superheated liquid,
discharged from the vent 12 into the conduit 16. Fluid discharged from
the vent 12 is initially conveyed upwardly through the conduit 16 due to
inertia. However, as will be appreciated, natural buoyancy encourages
fluid to rise upwardly through the conduit 16.

[0062]To reduce the heat loss from the heated fluid to the surrounding
sea, the conduit 16 is insulated. The hydrostatic pressure on the fluid
decreases as it travels upwardly through the conduit 16. At appropriate
temperature and pressure conditions, the fluid undergoes a phase change
from liquid to vapour. The level at which this phase change begins to
occur is indicated in FIG. 1 by the dashed line D. For the purposes of
this specification, this level is referred to as the "depth of
vapourization".

[0063]Each of the embodiments of the installation 10 shown in FIG. 1 is
arranged such that the upper end of the conduit 16 terminates below sea
level. Fluid exhausted from the upper end of each conduit 16 forms an
unconstrained plume, which mixes with sea water in the vicinity the upper
end of the respective conduit 16. The plume has a low density and is more
buoyant than sea water. Convective forces raise the plume and the
entrained sea water toward the sea surface S to create an upwelling,
which creates a mixing effect in the upper levels of the sea.

[0064]An unconstrained plume will attain a limiting height at which it
loses so much buoyancy by entrainment that it dissipates and spreads
horizontally.

[0065]In the embodiment illustrated in FIG. 1, the hood 14 is insulated to
minimize heat transfer from the superheated fluid discharged from the
respective vent 12, through the hood 14 to the surrounding sea water,
which can typically be in the range of 8-16° C. in the region of
hydrothermal vent "communities".

[0066]The hood 14 may be provided with an overflow discharge (not shown).

[0067]The overflow discharge enables excess fluid to escape the
installation 10 should the rate of flow of fluid entering the conduit 16
fall below the rate of flow of superheated fluid discharged from the
hydrothermal vent 12.

[0068]In certain embodiments, the overflow discharge can be in the form of
one or more holes located around the base of the hood.

[0069]As shown in FIG. 1, the conduits 16 of each of the three
installations are of different length. In addition, the upper ends of the
conduits 16 are arranged in an ascending sequence. An assembly (not
shown) of mooring lines, ballasts and buoyancy devices are used to
maintain the upper ends of the conduits 16 in the schematically
illustrated arrangement.

[0070]In the arrangement of FIG. 1, the three installations co-operate to
form a vertical set of unconstrained plumes. Specifically, the upper ends
of the insulated conduits 16 of the installations are arranged below the
sea surface to form a vertical set of plumes. That is, the plume formed
at the upper end of the deepest conduit 16c rises and mixes until it
dissipates. The upper end of the intermediate conduit 16b is positioned
to create a plume at the approximate depth of the limiting height of the
plume formed immediately below. Similarly, the plume formed at the upper
end of the intermediate conduit 16b rises and mixes until it dissipates.
The upper end of the intermediate conduit 16b is positioned to create a
plume at the approximate depth of the limiting height of the plume formed
immediately below. In this way, mixing of the sea from deeper levels into
the near-surface layer can be achieved.

[0071]The vertical separation of the upper ends of the conduits 16 can be
arranged such that fluid is exhausted from the shallowest and
intermediate conduits 16a, 16b at or near the limiting height of the
unconstrained plume formed by the conduit(s) at deeper levels.

[0072]Modelling of fluid flow through the conduit 16 indicates that the
depth of vapourization is predominantly dependent on the temperature of
fluid discharged from the vent and the vent depth. In addition, modelling
has made it evident that the fluid behaviour is almost independent of the
dimensions (length and diameter) of the conduit 16.

[0073]To determine depth of vapourization, amongst other operating
parameters of the sub-sea installation, a model was developed using
Bernoulli's Equation for compressible fluid flow. The following section
describes the development of such a model.

[0074]Primary assumptions were made regarding fluid behaviour in the
conduit. These assumptions include that fluid velocity in the conduit is
low, so velocity terms in the model can be ignored. Furthermore,
velocities are small, so that friction with the conduit walls can also be
neglected and the friction factor in the model can be assumed to be zero.
Accordingly, the model has been developed based on a hydrostatic
approximation.

[0075]Thermal conductivity losses are negligible since the conduit 16 is
well insulated, which means that thermal conductivity terms in the model
can also be ignored.

[0076]These assumptions reduce Bernoulli's Equation to:

##EQU00001##

[0077]in which: [0078]H is the specific enthalpy, [0079]z is the depth
(measured negatively downward), [0080]g is the acceleration due to
gravity, and [0081]d/dt is the total differential "moving with the
fluid".

[0082]Thus, specific enthalpy is related to depth by:

(Equation 2) [0083]in which H0 is the specific enthalpy at a
reference depth, z0.

[0089]Integrating Equation 6 with respect to p gives the specific volume,
V, in terms of internal energy, U, and pressure, p, as follows:

∫ ##EQU00005##

[0090]where V0 is the specific volume at a reference pressure,
p0.

[0091]In the domain of interest, the two phase domain, the temperature is
the saturation temperature which is a unique function of the pressure, as
follows:

T=Tsat(p) (Equation 8)

[0092]That is, the thermodynamic quantities, V, U and H, become functions
of the single variable, p, for both vapour and liquid phases. In
equilibrium, these quantities are each the weighted sum of the
corresponding vapour and liquid values. For example, specific energy is:

U=qUv+(1-q)Ul (Equation 9) [0093]in which: [0094]Uv is
the specific internal energy of the vapour phase, and [0095]Ul is
the specific internal energy of the liquid phase.

[0096]While Uv and Ul are known functions of the pressure for
the saturated mixture, the total specific internal energy, U, can only be
determined once the vapour mass fraction, is known. The mass vapour
fraction can be considered as a measure of the "quality", q, of the
steam.

[0097]The total enthalpy, H, given by Equation 1 can be assumed to be
constant for small changes in depth, and the steam quality, q, can then
be found from:

##EQU00006##

[0098]The steam quality, measured in this way, is used in Equation 9 to
determine the total specific internal energy, U, at each pressure level.

[0099]Thus, the specific volume, V, may be evaluated as a unique function
of the pressure using Equation 7. This may be integrated, in turn,
according to Equation 5 to give depth as a function of pressure, as
follows:

∫ ##EQU00007##

[0100]in which z0 is the depth of the reference pressure p0.

[0101]Thus, by iteration, the depth of vapourization, and values of
specific enthalpy, H, and steam quality, q, can be determined.

[0102]The model can be used to estimate the following fluid properties,
each as a function of depth below sea level, within the conduit 16:
[0103]1. Internal pressure, which can provide pressure at the upper end
of the conduit 16; [0104]2. Temperature, which can provide temperature at
the upper end of the conduit 16; [0105]3. Specific Volume, from which
information regarding the density of fluid, and fluid velocity on
exhausted from the upper end of the conduit 16 can be obtained; and
[0106]4. Steam quality.

[0107]The above four fluid properties can be used to determine performance
parameters of the desired application of the installation 10.

[0108]FIGS. 2 to 5 show indicative values of the above four fluid
properties for an installation according to an embodiment of the present
invention for each of three hypothetical natural hydrothermal vents
located in the sea at a depth of 200 metres below sea level. The three
vents have discharge temperatures of 170° C., 190° C. and
210° C. The installation includes a load that receives fluid
discharged from the insulated conduit. The fluid properties shown in each
of FIGS. 2 to 5 have been calculated using the above described model.

[0110]In each of FIGS. 3 and 4, the depth of vapourization can be readily
observed as a discontinuity in the curve of each respective vent. The
approximate depth of vapourization for each of the three hypothetical
vents, located at a depth of 200 m below sea level, is set out in the
following table.

[0111]FIGS. 6 to 9 show indicative values of the above four fluid
properties for an installation according to an embodiment of the present
invention for each of four hypothetical natural hydrothermal vents that
are located in the sea at a depth of 2500 metres below sea level. The
four vents have discharge temperatures of 300° C., 320° C.,
340° C. and 360° C. The installation includes a load that
receives fluid discharged from the insulated conduit. The fluid
properties shown in each of FIGS. 6 to 9 have been calculated using the
above described model.

[0113]In each of FIGS. 7 and 8, the depth of vapourization can be readily
observed as a discontinuity in the curve of each respective vent. The
approximate depth of vapourization for each of the four hypothetical
vents, located at a depth of 2500 m below sea level, is set out in the
following table.

[0114]The analytical modelling as described above leads to some important
consequences for applications of sub-sea installations according to
embodiments of the present invention, which utilize the power of an
underwater hydrothermal vent. These include the following: [0115]Fluid
pressures within the conduit 16 at sea level are generally high,
particularly for vents of depths in the order of 2500 metres below sea
level. [0116]Fluid temperatures within the conduit 16 at sea level are
acceptable for heat-engine input. [0117]The steam quality is very low
(less than 20% at sea level, and as low as 2% for shallow, low
temperature vents). For a vent at depth of 2500 metres with a discharge
temperature of 280° C., no phase change occurs (that is, the steam
quality is zero at sea level). [0118]There is a steady increase in the
pressure difference between the interior and exterior of the conduit 16
with decreasing depth. [0119]There is a large differential specific
volume (between the ends of the conduit in an installation) for shallow
depth, low temperature vents. Hence, if the cross section of the conduit
is constant, there would be a corresponding large differential in fluid
velocity.

[0120]FIG. 10 shows an installation 110 in accordance with a second
embodiment of the present invention. The installation 110 is arranged to
convey superheated fluid discharged from a vent 112 located at the base
of a body of water. In this embodiment, the body of water is the sea, and
the vent 112 is a natural hydrothermal vent located on the sea floor. The
installation has a hood 114 for locating the installation 110 over the
vent. A conduit 116 in fluid communication with the hood 114 extends
upwardly through the sea towards the sea surface S.

[0121]The hood 114 anchors the lower end of the conduit 116 over the vent
112 and directs fluid discharged from the vent 112 into the conduit 116.
Fluid discharged from the vent 112 is initially conveyed upwardly through
the conduit 116 due to inertia. However, as will be appreciated, natural
buoyancy encourages fluid to rise upwardly through the conduit 116.

[0122]To reduce the heat loss from the heated fluid to the surrounding
sea, the conduit 116 is insulated. At appropriate temperature and
pressure conditions, the fluid undergoes a phase change from liquid to
vapour. The depth of vapourization is indicated in FIG. 10 by the dashed
line D.

[0123]The installation 110 shown in FIG. 10 is arranged such that the
upper end of the conduit 116 continues through the sea surface S and
feeds into a heat engine 118, which in this embodiment is located on dry
land. The heat engine 118 converts thermal energy within the fluid
exhausted from the conduit 116 into mechanical motion that can be used to
generate electricity by means of an electric generator 120.

[0124]In this embodiment, the conduit 116 is in the form of a series of
cylindrical sections 122a, 122b, 122c, 122d (hereinafter referred to
collectively as cylindrical sections 122) that are interconnected by
conical sections 124a, 124b, 124c (hereinafter referred to collectively
as conical sections 124). The series is arranged such that the inner
diameter of the cylindrical sections 122 increases with proximity to the
sea surface.

[0125]The lowermost cylindrical section 122a is connected at its lower end
to the hood 114, and at its upper end to the lowermost conical section
124a. As shown in FIG. 10, the upper end of the lowermost cylindrical
section 122a terminates at the depth of vapourization D.

[0126]As the water rises in the lowermost section 122a of the conduit 116,
the hydrostatic pressure decreases. At the depth of vapourization the
fluid begins to boil. The resulting two phase fluid continues to rise in
conical section 124a, which has an internal diameter increasing with
decreasing depth. Conical section 124a maintains the velocity of the
fluid approximately constant while its specific volume increases with
decreasing hydrostatic pressure. Conical section 124a is joined to a
further cylindrical section 122b, which has a larger cross-sectional area
compared to the lowermost cylindrical section 122a. Thus, the series of
cylindrical sections 122 and the conical sections 124 are configured to
maintain an approximately constant fluid velocity within the conduit 116.

[0127]As the two phase fluid rises further in the conduit 116, the liquid
phase continues to boil and the fraction of vapour by mass (that is, the
steam quality) continues to increase. The increasing steam quality and
decreasing pressure cause the specific volume of the two phase fluid to
increase still further.

[0128]In the embodiment illustrated in FIG. 10, the hood 114 is insulated
to minimize heat transfer from the superheated fluid discharged from the
respective vent 112, through the hood 114 to the surrounding sea water,
which can typically be in the range of 2-16° C. in the region of
hydrothermal vent "communities".

[0129]The hood 114 may be provided with an overflow discharge (not shown).
The overflow discharge enables excess fluid to escape the installation
110 should the rate of flow of fluid entering the conduit 116 fall below
the rate of flow of superheated fluid discharged from the hydrothermal
vent 112.

[0130]In certain embodiments, the overflow discharge can be in the form of
one or more holes located around the base of the hood.

[0131]In certain conditions, such as those associated with shallower
vents, a resonant behaviour may be established in the fluid column within
the conduit, in which the fluid column resembles a Helmholtz resonator or
a spring pendulum. The resonant behaviour is created by a length of
liquid lower regions of the conduit or so leads into a vapour containing
region further up the conduit. The length of liquid can be considered to
be a "plug" of high inertia, and the vapour above the liquid being
considered to be a "spring".

[0132]If the resonant behaviour causes the liquid "plug" to oscillate in
the conduit, the result can be catastrophic damage of the conduit or heat
engine. To minimize such resonant behaviour, the friction term (from wall
friction within the conduit) in the equation of motion must exceed the
value required for critical damping. This can be achieved by decreasing
the cross-section of the conduit, which results in an increase in the
velocity of the fluid flow. If the velocity is increased sufficiently,
the friction is of sufficient magnitude compared to the hydrostatic and
thermodynamic terms to bring about critical damping.

[0133]However, narrowing the entire length of the conduit to this extent
can create further problems where the greater specific volume results in
proportionally greater velocity. High velocity flow in the conduit may
lead to feedback between pressure drop and phase changes. Such feedback
is likely to bring about chaotic behaviour with regard to pressure within
the conduit and erratic phase changes.

[0134]Increasing the cross-section area of the conduit 116 above the depth
of vapourization will maintain a roughly constant fluid velocity within
the conduit.

[0135]This minimizes the likelihood of pressure and phase change
irregularities. In the embodiment shown in FIG. 10, the series of
cylindrical sections 122 and conical sections 124 form a "piecewise
flaring" of the conduit 116 towards the sea surface, which serves to keep
the fluid velocity within a narrow range that can be considered roughly
constant.

[0136]In alternative embodiments of the installation, the conduit may be
continuously flared above the depth of vapourization.

[0137]In certain conditions, such as those associated with deeper vents, a
large pressure difference across the wall of the conduit is experienced
above the depth of vapourization. For example, in an installation
connected to a vent at 2500 metres that has a discharge temperature of
360° C., the pressure differential can be as much as 15 mPa. In
installations for these applications, the conduit 116 can be constructed
such that the series of cylindrical sections and the conical sections
have increasing pressure tolerance with proximity to the sea surface. In
some embodiments, this can be achieved by increasing the wall thickness
of the series of cylindrical sections and the conical sections.
Alternatively or additionally, this can be achieved by selection of
materials that are used to construct the conduit 116.

[0138]As shown in FIG. 10, the installation 110 has a series of buoys 126
and anchors 128 attached to the conduit 116 to maintain the conduit 116
in a generally constant configuration. The buoys 126 and anchors 128 work
against movement of the sea caused by ocean currents and the like, and
any changes in buoyancy of the conduit 116 caused by changing fluid
conditions in the conduit 116.

[0139]During installation, the hood 114 will need to be manoeuvred into
position over the vent 112. The hood 114 has buoyancy tanks 130 that
facilitate handling during this operation. The buoyancy tanks 130 can be
filled with a buoyant fluid that is more buoyant than sea water
surrounding the vent 112. This buoyant fluid can be any one or a mixture
of: gases, liquid hydrocarbons, and sea water. Once the hood 112 is in
the correct position, the buoyant fluid can be expelled from the tanks
130.

[0140]The hood 112 also has ballasts 132 that are attached to a lower part
of the hood 112. The ballasts 132 work to hold the hood 112 firmly in
position and prevent dislodgement due to the stresses of ocean currents.

[0141]FIG. 11 shows an installation 210 in accordance with a third
embodiment of the present invention. The installation 210 is arranged to
convey superheated fluid discharged from a vent 212 located at the base
of a body of water. In this embodiment, the body of water is the sea, and
the vent 212 is a natural hydrothermal vent located on the sea floor. The
installation has a hood 214 for locating the installation 210 over the
vent 212. A conduit 216 in fluid communication with the hood 214 extends
upwardly through the sea towards the sea surface S.

[0142]The hood 214 anchors the lower end of the conduit 216 over the vent
212 and directs fluid discharged from the vent 212 into the conduit 216.
Fluid discharged from the vent 212 is initially conveyed upwardly through
the conduit 216 due to inertia. However, as will be appreciated, natural
buoyancy encourages fluid to rise upwardly through the conduit 216.

[0143]To reduce the heat loss from the heated fluid to the surrounding
sea, the conduit 216 is insulated. At appropriate temperature and
pressure conditions, the fluid undergoes a phase change from liquid to
vapour. The depth of vapourization is indicated in FIG. 11 by the dashed
line D.

[0144]In the embodiment illustrated in FIG. 11, the hood 214 is insulated
to minimize heat transfer from the superheated fluid discharged from the
respective vent 212, through the hood 214 to the surrounding sea water,
which can typically be in the range of 2-16° C. in the region of
hydrothermal vent "communities".

[0145]The hood 214 may be provided with an overflow discharge (not shown).
The overflow discharge enables excess fluid to escape the installation
210 should the rate of flow of fluid entering the conduit 216 fall below
the rate of flow of superheated fluid discharged from the hydrothermal
vent 212.

[0146]In certain embodiments, the overflow discharge can be in the form of
one or more holes located around the base of the hood.

[0147]In this embodiment, the conduit 216 is in the form of a series of
cylindrical sections 222a, 222b (hereinafter referred to collectively as
cylindrical sections 222) and an interconnecting conical section 224. The
series is arranged such that the inner diameter of the cylindrical
sections 222 increases with proximity to the sea surface.

[0148]The lowermost cylindrical section 222a is connected at its lower end
to the hood 214, and at its upper end to the conical section 224. As
shown in FIG. 11, the upper end of the lowermost cylindrical section 222a
terminates at the depth of vapourization D.

[0149]As the water rises in the lowermost section 222a of the conduit 216,
the hydrostatic pressure decreases. At the depth of vapourization the
fluid begins to boil. The resulting two phase fluid continues to rise in
the conical section 224, which has an internal diameter increasing with
decreasing depth. Conical section 224 maintains the velocity of the fluid
approximately constant while its specific volume increases with
decreasing hydrostatic pressure. Conical section 224 is joined to a
further cylindrical section 222b, which has a larger cross-sectional area
compared to the lowermost cylindrical section 222a.

[0150]The installation 210 has a series of buoys 226 and anchors 228
attached to the conduit 216 to maintain the conduit 216 in a generally
constant configuration. The buoys 226 and anchors 228 work against
movement of the sea caused by ocean currents and the like, and any
changes in buoyancy of the conduit 216 caused by changing fluid
conditions in the conduit 216.

[0151]The hood 212 also has buoyancy tanks 230 and ballasts 232 that
operate in the manner of the buoyancy tanks 130 and ballasts 132
described in connection with the embodiment illustrated in FIG. 10.

[0152]The installation 210 further includes a bubble pump 240, which is
located beneath the sea surface S. The bubble pump 240 is essentially a
thin-walled conduit formed of a sea water impervious membrane. The inner
diameter of the bubble pump 240 that is significantly greater than that
of the upper end of the insulated conduit 216. The bubble pump 240 is
arranged with its open ends arranged in approximately vertical alignment.

[0153]A series of buoys 242 and anchors 244 are attached to the ends of
the bubble pump 240. The buoys 242 and anchors 244 work to maintain the
bubble pump 240 in the approximate orientation illustrated in FIG. 11.

[0154]The upper end of the insulated conduit 216 terminates within the
bubble pump 240. Fluid exhausted from the insulated conduit 216 drives
the bubble pump 240. In particular, the fluid exhausted from the
insulated conduit 216 forms a plume that has a relatively low density
compared with the sea water immediately surrounding the upper end of the
insulated conduit 216. Convective forces raise the plume toward the sea
surface S. Movement of the plume draws water into the lower end of the
bubble pump 240 to create an upward flow of water through the bubble pump
240.

[0155]The function of the bubble pump 240 is to contain the plume of
low-density two-phase fluid and so inhibit mixing with colder sea water.
Thus, the maximum height of the plume can be increased by controlling
the mixing with sea water.

[0156]The cold water brought up from below the bubble pump 240 exits the
bubble pump 240 and mixes into the upper, stratified layers of the ocean
known as "the mixed layer" or the "euphotic zone".

[0157]In many parts of the ocean, deeper water is richer in nutrients such
as nitrates, phosphates, iron and silicon than is the euphotic zone,
which is largely depleted of nutrients. Mixing water from these deeper
layers into the euphotic zone will cause biological productivity to
increase in the manner observed in a naturally occurring ocean upwelling
because deep-lying nutrients are brought into the euphotic zone where
light is available for photosynthesis.

[0158]Thus, the installation 240 generates an artificial upwelling that
increases biological productivity in the same way as a natural upwelling.
This increased productivity will either enhance an existing marine
ecosystem or cause a new marine ecosystem 250 to come into existence and
be continuously maintained as long as the installation 210 is in
operation.

[0159]The bubble pump 240 is able to move very large volumes of sea water
because the density of steam is orders of magnitude less than the density
differences of the sea water being pumped. Hence the potential energy
provided by unit mass of steam at depth is orders of magnitude greater
than the potential energy required to raise unit mass of sea water. A
small amount of steam is able to raise a very large amount of sea water.
It is envisaged that an installation 210 located over a 10 MW
hydrothermal vent can generate upwelling flows through the bubble pump
240 of the order of milli-Sverdrups, which is the flow rate of a
medium-sized river.

[0160]A typical bubble pump 240 could have an internal diameter of the
order of 10 metres. The upper end of such a bubble pump 240 would be
disposed at a depth of approximately 5 to 10 metres.

[0161]The depth of the lower end of the bubble pump 240 is preferably
within the layers of the sea that are the richest with regard to the
desired nutrients. In shallow vent applications, this depth may be
limited by the sea bed. In deep vent applications, the depth of the lower
end is likely to be in the region of 800 to 1000 metres.

[0162]The installation 240, when operated in a region where high nutrient
concentrations and high alkalinity occur at depth, can also cause
carbon-dioxide to be removed from the atmosphere. Photosynthesis takes
place as a consequence of the increase in nutrients close to the surface
where sunlight is available. The carbon is immediately taken up by the
biomass, which is likely to be primarily plankton. Over time it becomes
sequestered in the deep ocean for millennia and, more permanently, in
sediment on the ocean floor when detritus falls out of the artificial
marine ecosystem that has been created. The embodiment can also have the
effects of cooling the surface layer of the ocean and decreasing its
acidity. Increased alkalinity of the mixed layer also results in carbon
dioxide being removed from the atmosphere due to its increased solubility
with the sea water.

[0163]Some embodiments of the invention provide a method of conveying
thermal energy from a vent located at the base of a body of water, the
vent discharging superheated fluid. The method involves: [0164]a)
installing an installation over the hydrothermal vent, the installation
comprising a hood that is in fluid communication with an insulated
conduit, such that superheated fluid discharged from the vent is directed
by the hood into the insulated conduit; and [0165]b) conveying fluid
upwardly in the insulated conduit and through the body of water.

[0166]In step (b), fluid can be conveyed in a manner such that the fluid
at least partly vapourizes as it rises within the conduit. In this way,
fluid that is exhausted from the upper end of the insulated conduit is at
least a two-phase fluid.

[0167]It will be appreciated that the body of water can be the sea, a
natural/man-made lake, or a water-filled subterranean cavity.

[0168]Two or more installations according to the embodiment described in
connection with FIG. 1 can be arranged such that the hood of each
installation is located over an individual vent. The upper ends of the
insulated conduits of the installations can be arranged below the sea
surface to form a horizontal array of plumes.

[0169]It will be understood to persons skilled in the art of the invention
that many modifications may be made without departing from the spirit and
scope of the invention.

[0170]In the claims which follow and in the preceding description of the
invention, except where the context requires otherwise due to express
language or necessary implication, the word "comprise" or variations such
as "comprises" or "comprising" is used in an inclusive sense, i.e. to
specify the presence of the stated features but not to preclude the
presence or addition of further features in various embodiments of the
invention.